/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.gson;

import java.io.IOException;
import java.io.StringWriter;
import java.math.BigDecimal;
import java.math.BigInteger;

import com.google.gson.internal.Streams;
import com.google.gson.stream.JsonWriter;

/**
 * A class representing an element of Json. It could either be a {@link JsonObject}, a
 * {@link JsonArray}, a {@link JsonPrimitive} or a {@link JsonNull}.
 *
 * @author Inderjeet Singh
 * @author Joel Leitch
 */
public abstract class JsonElement {
    /**
     * Returns a deep copy of this element. Immutable elements like primitives
     * and nulls are not copied.
     */
    abstract JsonElement deepCopy();

    /**
     * provides check for verifying if this element is an array or not.
     *
     * @return true if this element is of type {@link JsonArray}, false otherwise.
     */
    public boolean isJsonArray() {
        return this instanceof JsonArray;
    }

    /**
     * provides check for verifying if this element is a Json object or not.
     *
     * @return true if this element is of type {@link JsonObject}, false otherwise.
     */
    public boolean isJsonObject() {
        return this instanceof JsonObject;
    }

    /**
     * provides check for verifying if this element is a primitive or not.
     *
     * @return true if this element is of type {@link JsonPrimitive}, false otherwise.
     */
    public boolean isJsonPrimitive() {
        return this instanceof JsonPrimitive;
    }

    /**
     * provides check for verifying if this element represents a null value or not.
     *
     * @return true if this element is of type {@link JsonNull}, false otherwise.
     * @since 1.2
     */
    public boolean isJsonNull() {
        return this instanceof JsonNull;
    }

    /**
     * convenience method to get this element as a {@link JsonObject}. If the element is of some
     * other type, a {@link IllegalStateException} will result. Hence it is best to use this method
     * after ensuring that this element is of the desired type by calling {@link #isJsonObject()}
     * first.
     *
     * @return get this element as a {@link JsonObject}.
     * @throws IllegalStateException if the element is of another type.
     */
    public JsonObject getAsJsonObject() {
        if (isJsonObject()) {
            return (JsonObject) this;
        }
        throw new IllegalStateException("Not a JSON Object: " + this);
    }

    /**
     * convenience method to get this element as a {@link JsonArray}. If the element is of some
     * other type, a {@link IllegalStateException} will result. Hence it is best to use this method
     * after ensuring that this element is of the desired type by calling {@link #isJsonArray()}
     * first.
     *
     * @return get this element as a {@link JsonArray}.
     * @throws IllegalStateException if the element is of another type.
     */
    public JsonArray getAsJsonArray() {
        if (isJsonArray()) {
            return (JsonArray) this;
        }
        throw new IllegalStateException("This is not a JSON Array.");
    }

    /**
     * convenience method to get this element as a {@link JsonPrimitive}. If the element is of some
     * other type, a {@link IllegalStateException} will result. Hence it is best to use this method
     * after ensuring that this element is of the desired type by calling {@link #isJsonPrimitive()}
     * first.
     *
     * @return get this element as a {@link JsonPrimitive}.
     * @throws IllegalStateException if the element is of another type.
     */
    public JsonPrimitive getAsJsonPrimitive() {
        if (isJsonPrimitive()) {
            return (JsonPrimitive) this;
        }
        throw new IllegalStateException("This is not a JSON Primitive.");
    }

    /**
     * convenience method to get this element as a {@link JsonNull}. If the element is of some
     * other type, a {@link IllegalStateException} will result. Hence it is best to use this method
     * after ensuring that this element is of the desired type by calling {@link #isJsonNull()}
     * first.
     *
     * @return get this element as a {@link JsonNull}.
     * @throws IllegalStateException if the element is of another type.
     * @since 1.2
     */
    public JsonNull getAsJsonNull() {
        if (isJsonNull()) {
            return (JsonNull) this;
        }
        throw new IllegalStateException("This is not a JSON Null.");
    }

    /**
     * convenience method to get this element as a boolean value.
     *
     * @return get this element as a primitive boolean value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               boolean value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public boolean getAsBoolean() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a {@link Boolean} value.
     *
     * @return get this element as a {@link Boolean} value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               boolean value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    Boolean getAsBooleanWrapper() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a {@link Number}.
     *
     * @return get this element as a {@link Number}.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               number.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public Number getAsNumber() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a string value.
     *
     * @return get this element as a string value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               string value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public String getAsString() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a primitive double value.
     *
     * @return get this element as a primitive double value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               double value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public double getAsDouble() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a primitive float value.
     *
     * @return get this element as a primitive float value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               float value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public float getAsFloat() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a primitive long value.
     *
     * @return get this element as a primitive long value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               long value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public long getAsLong() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a primitive integer value.
     *
     * @return get this element as a primitive integer value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               integer value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public int getAsInt() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a primitive byte value.
     *
     * @return get this element as a primitive byte value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               byte value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     * @since 1.3
     */
    public byte getAsByte() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a primitive character value.
     *
     * @return get this element as a primitive char value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               char value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     * @since 1.3
     */
    public char getAsCharacter() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a {@link BigDecimal}.
     *
     * @return get this element as a {@link BigDecimal}.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive}.
     *                               * @throws NumberFormatException if the element is not a valid {@link BigDecimal}.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     * @since 1.2
     */
    public BigDecimal getAsBigDecimal() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a {@link BigInteger}.
     *
     * @return get this element as a {@link BigInteger}.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive}.
     * @throws NumberFormatException if the element is not a valid {@link BigInteger}.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     * @since 1.2
     */
    public BigInteger getAsBigInteger() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * convenience method to get this element as a primitive short value.
     *
     * @return get this element as a primitive short value.
     * @throws ClassCastException    if the element is of not a {@link JsonPrimitive} and is not a valid
     *                               short value.
     * @throws IllegalStateException if the element is of the type {@link JsonArray} but contains
     *                               more than a single element.
     */
    public short getAsShort() {
        throw new UnsupportedOperationException(getClass().getSimpleName());
    }

    /**
     * Returns a String representation of this element.
     */
    @Override
    public String toString() {
        try {
            StringWriter stringWriter = new StringWriter();
            JsonWriter jsonWriter = new JsonWriter(stringWriter);
            jsonWriter.setLenient(true);
            Streams.write(this, jsonWriter);
            return stringWriter.toString();
        } catch (IOException e) {
            throw new AssertionError(e);
        }
    }
}
